Repeaters and relays are efficient for both providing coverage in areas without coverage and also to provide increased data rates to areas with weak signal strength for example at cell edge and indoor. A repeater works in the physical layer and amplifies and forwards the signal, including present noise and interference. A relay typically decodes the data before amplifying and forwarding the signal, which means that interference and noise will not be forwarded.
Repeaters and relays are usually served by a base station called donor base station, and usually serve user terminals. If the antenna at the repeater or relay intended for communication with the donor base station is reconfigurable, for example by means of beam-forming, the donor base station could be changed by pointing the beam of the reconfigurable antenna from the current donor base station to another base station. The reason for doing this could for example be that the current donor base station is overloaded or breaks down.
Repeaters and relays that are placed on moving objects like for example trains or ships are called mobile relays. A mobile relays must change donor base station due to that the train and ships will move from one cell to another.
When using a reconfigurable antenna at repeaters or relays for changing the donor base station, some kind of handover is required. For a repeater, all the user terminals served by that repeater must make a handover from the current donor base station to the new donor base station. If the change of donor base station becomes too quick, all the user terminals will not have time required to do these handovers and connections will be dropped. For a relay, the user terminals that are served by that relay do not have to make handovers due to that they are connected to the relay regardless of which donor base station the relay got. That is, the donor base station is transparent to the user terminals since the relay acts like a base station. However, the relay itself has to make a handover from the current donor base station to the new donor base station.
US 2006229076 discloses a wireless communication terminal on a mobile platform, such as a train, that makes use of directional antennas able to accomplish soft handoffs between base transceiver stations. An antenna controller controls a beam-forming network to generate a first and a second lobe, the first lobe being directed towards a donor base station and the second lobe being used to continuously scan for one or more different base transceiver stations sites that may be available to form a higher quality link.
However, it is difficult to maintain coverage for the first lobe while having a desired flexibility with the second lobe. Furthermore, if the second lobe suddenly finds a different base transceiver station, there will be a lot of interference in the radio.
It is therefore a desire to provide a repeater or a relay with an improved handover when changing donor base station for relay and repeater compared with prior art.